Users have multiple telecommunication devices such as cellular phones, tablet computers, laptops, and other devices. Each device may have its own communication address, such as a telephone number, and may receive communications directed to any communication address associated with a service account.
In (IP) Multimedia Subsystem (IMS), call forking may be achieved through implicit registration sets (IRS). With IRS, when any one network identity (e.g., IP Multimedia Public Identifier (IMPU)) associated with a communication address is registered, other network identities associated with a same service account as that network identity are also registered. When a communication is received and directed to any one network identity of the registration set, it may be sent to all network identities of that registration set.
Session Initiation Protocol (SIP), as extended by RFC 3265 (“Session Initiation Protocol (SIP)-Specific Event Notification”, June 2002), utilizes a subscribe method to request a current state as well as state updates from a remote node. The specification for Open Mobile Alliance (OMA) Presence SIMPLE (SIP for Instant Messaging and Presence Leveraging Extensions) defines mechanisms for utilizing SIP to perform instant messaging and other functions. Rich Communication Services (RCS) is a GSM Association (GSMA) program that provides for inter-operability within an IP Multimedia Subsystem (IMS). One feature of RCS is the ability to discover capabilities of contacts. RCS utilizes OMA SIMPLE for various features, including subscription to a presence server to obtain capability information for a list of contacts.